Scanners to examine logs, center cants, and flitches, and computers to analyze the data from the scanners and determine the optimum cutting pattern, have been in use in saw mills for many years. A scanner and computer system first determines the lumber that can be produced from a log, and from that information, the optimum cutting of the log into a center cant and flitches (the slices of wood from each side of the center cant having a determined thickness but meandering width). The center cant is directed to one operation to be analyzed and cut into dimensional lumber of one type, and the flitches are directed to another operation to be analyzed and cut into dimensional lumber of varying types.
With respect to this secondary operation of analyzing and cutting the flitches, the flitches have a specific, determined thickness but have a non-determined and inconsistent width. The side edges that define the width are a result of the original configuration of the log. Because the flitches are simply untrimmed slices from the log, the side edges are sections of the log's periphery. Because the slices are taken off center (to one side or the other of the center cant), the edges are angled relative to the side faces and one face is slightly smaller in area that the other. These angled edges are not straight (they meander) and they are not parallel to each other, (they tend to diverge) a result of the conical configuration of a log. (Hereafter these edges will be referred to as wane edges.)
It is well-known that very small gains in log utilization make substantial differences in saw mill economy. Thus an important aspect of the scanning and computer systems as applied to flitches is to fit the maximum number of pieces (of highest value) into the available surface area of a flitch. In many instances, a lumber piece will not quite fit the smaller of the two faces but will the larger; i.e., in the smaller face the side edge of the proposed piece extends over the angled wane edge. However, the rules applied to acceptability for dimensional lumber permit a limited amount of this wane edge to be embodied in a finished lumber piece. The lumber piece that extends over the wane edge has to be an exact full width in profile whereby the side edges of the lumber piece are complete lengthwise along the entire length of that piece. That is, the corner where the smaller face and side edge meet can be somewhat "rounded" but at least a portion of the side edge must extend along the entire length of the piece in a straight line. Obviously if the lumber piece is fit totally to the larger face, the edge will be complete along that face.
Whereas scanning and computer technology has been developed to accommodate the problem of fitting the maximum number of specifically dimensioned lumber pieces to a flitch, a different problem arises when the flitches are to be cut into grade lumber; e.g., lumber to be used for door frames, trim, furniture, and the like. That is because the rules for acceptability are different. Whereas a width will be designated, the width can typically vary plus or minus 0.5 inch. That is, they have random widths and are sold, e.g. as a 6-inch wide board even though the the board may be a true width of anywhere between 5.5-inches and 6.5-inches. etc.
Furthermore, grade lumber will be graded depending on the "flaws" visually apparent in the wood; e.g., knots, splits, nicks, etc. (A flaw is any visual abnormality determined undesirable for that particular grade of lumber.) Within a given flitch it may be desirable to cut certain widths out of the board for high-grade, the remaining widths having the flaws) being designated of lower-grade. Whereas the scanning systems are not capable of detecting these visual flaws, an operator will identify the flawed areas and designate sections of higher or lower grade lumber. This designation forces into the system a saw line that must then be accommodated by the system. (Referred to as a "forced-board" fitting.)
Finally, there is area wane. For grade lumber, area wane is the area of the face of a proposed board (the smaller face) that does not fill out the precise rectangular area of designated width and length. (This is not be confused with wane edge, but as will be explained, the existence of wane edge is encompassed as a part of area wane.) Contrary to the rules for dimensional lumber, the profile of grade lumber does not have to be a complete rectangle; i.e., edge portions can have voids. Whether there is a void or simply a wane edge, whatever is missing from the rectangular surface area is area wane and must be calculated as a percentage of the designated dimensional area. The rules for grade lumber designate the acceptable percentage of area wane for different grades.